Upon stimulation by a steroid hormone, the glucocorticoid receptor moves from the cytoplasm to specific sites in the nucleus, but the mechanism of this transport either within the cytoplasm or within the nucleus is unknown. To address these issues, we are using time-lapse microscopy to visualize and quantify the receptor translocation process. Fluorescence recovery after photobleaching (FRAP) is being used to assess receptor mobility both in the cytoplasm and in the nucleus before and after hormone treatment. To visualize the motion of a small number of receptor molecules, receptor-coated fluorescent beads are microinjected into tissue culture cells. The bead motion is followed by time-lapse 3D microscopy.